PARIS — French gendarmes say workers paid to demolish an uninhabited house in Brittany made an unexpected discovery in the cellar — 600 gold coins.

The Pont-Aven gendarmerie said Monday that after rattling a mysterious, shell-shaped container, the workers discovered the coins inside. They were Belgian, dated 1870, and bore the face of the then-reigning king of Belgium, Leopold II.

The gendarmerie said the workers reported the discovery and the treasure has since been put under lock and key until more information is unearthed about its provenance.